Forward-reverse powershift control

ABSTRACT

Disclosed is an automatic control system for a powershift, preselect transmission (10) including a plurality of power paths (36, 38) alternately connectable between input (12) and output (20) shafts by first engaging selected ones of synchronizer clutches (42, 74, 84) associated with each of a plurality speed ratio gears (44, 46, 76, 78, 80) in each path and then alternately engaging a powershift clutch (48, 82) associated with each path. The control system includes a hydraulic logic system (118) which may be electronic and a hydraulic and shift valve system which may be electrically controlled should the logic be electronic. The control system preselects ratio gears in a nondriving path and then alternately engages the powershift clutches to switch driving connections from one path to the other. The logic system includes an improved reverse sequence valve (132) and improved shift valves (124, 126, 128). The shift valve system includes the feature of trimmer valves (364, 370, 372, 374) to control the engagement rate of the synchronizer clutches and combination trimmer valves (360, 366) to control the engagement rate of the powershift clutches.

CROSS-REFERENCE TO RELATED APPLICATION

The invention of this application relates to U.S. Pat. No. 4,246,993;U.S. Application Ser. No. 178,429, filed Aug. 15, 1980, now U.S. Pat.No. 4,375,171; and U.S. Application Ser. Nos. 331,391, 331,392, 331,393,331,394, 331,396, 331,397, all filed Dec. 16, 1981. All of the above areassigned to the assignee of this application and all are incorporatedherein by reference.

FIELD OF THE INVENTION

The invention relates to a transmission control to effect powershiftingbetween forward and reverse. More specifically, the invention relates toa fluid or hydraulic control having a reverse sequence valve to effectforward and reverse powershifting.

BACKGROUND OF THE INVENTION

Preselect, powershift transmissions of the type having a plurality ofmultiple ratio power paths alternately connected between input andoutput shafts are well-known. Such transmissions are well-suited forroad vehicles since they may be made relatively compact and inexpensiveand since they may be readily powershifted by both manual and automaticcontrols. Many of these transmissions include two countershafts eachdefining a power path, two or more ratio gears rotatably mounted on eachcountershaft with at least one of the gears on one countershaft being areverse gear and with all of the gears in constant driving relation withthe output shaft, a synchronizer clutch associated with each gear andengagable to clutch one gear at a time to each respective countershaft,and two powershift clutches alternately engaged to complete drivingconnections between the input and output shafts.

Controls for such transmissions (particularly automatic controls)readily provide for automatic, power upshifting and downshifting in theforward speed ratios by establishing a driving connection through onepath, engaging or preselecting the next upshift or downshift ratio gearin the other or nondriving path, then switching the driving connectionfrom the one path to the other path by substantially simultaneouslyengaging and disengaging the powershift clutches respectively associatedwith the other path and the one path.

However, controls of such transmissions have not readily provided forpowershifting between forward and reverse Powershifting between forwardand reverse has many advantages, particularly when the transmission isinstalled in a vehicle which may be occasionally stuck in snow or mud.

SUMMARY OF THE INVENTION

An object of this invention is to provide a control for powershifting apreselect transmission between forward and reverse.

According to a feature of the invention, a transmission includes aplurality of multiple ratio gear power paths alternately connectablebetween input and output shafts by first engaging selected ones ofclutch means associated with each gear and then alternately engaging apowershift clutch associated with each path in response to an improvedcontrol system including a shift selector moveable between forward,neutral, and reverse drive positions; signal means providing a speedsignal proportional to the output shaft speed; and a hydraulic orelectrical reverse sequence device shiftable between states respectivelyeffecting engagement and disengagement of the clutch means associatedwith a reverse speed ratio gear of another path and operative onceshifted into the engagement state to remain therein while the speedsignal is below a predetermined magnitude and independent of changes inthe position of the shift selector.

According to a feature of the invention, a transmission includes aplurality of multiple ratio gear power paths alternately connectablebetween input and output shafts by first engaging selected ones ofclutch means associated with each gear and then alternately engaging apowershift clutch associated with each path in response to an improvedcontrol system including a shift selector moveable between forward,neutral, and reverse positions; a signal means providing a speed signalproportional to the output shaft speed; hydraulic or electrical devicesfor selectively engaging the clutch means and alternately engaging thepowershift clutches in response to the position of the selector andchanges in the magnitude of the speed signal; hydraulic or electricaldevices for engaging the clutch means associated with a forward speedratio gear of one path independent of the shift selector position; and ahydraulic or electrical reverse sequence device shiftable between statesrespectively effecting engagement and disengagement of the clutch meansassociated with a reverse speed ratio gear of another path and operativeonce shifted into the engagement state to remain therein while the speedsignal is below a predetermined magnitude and independent of changes inthe position of the shift selector.

BRIEF DESCRIPTION OF THE DRAWINGS

A preselect transmission and a control system therefore is illustratedin the accompanying drawings in which:

FIG. I is a schematic view of the transmission, looking in the directionof arrows I--I in FIG. II;

FIG. II is a schematic view of the transmission, looking in thedirection of arrows II--II in FIG. I;

FIG. III is a somewhat schematic view of a hydraulic logic system of thetransmission control system;

FIGS. III-A and III-B are enlarged views of several of the valves inFIG. III;

FIG. IV is a somewhat schematic view of a shift valve system of thecontrol system;

FIGS. IV-A through IV-F are enlarged views of several of the valves inFIG. IV;

FIGS. V and VI schematically illustrate pressure rise curves or pressurerise paths of trimmer valves in FIGS. IV, IV-E, and IV-F; and

FIG. VII is an alternative embodiment of a trimmer shown in FIGS. IV andIV-F.

Certain terminology referring to environment and specific types ofcomponents, direction, motion, and relationship of components to eachother will be used in the following description. This terminology is forconvenience in describing the invention and should not be consideredlimiting unless it is explicitly used in the claims.

DETAILED DESCRIPTION OF THE DRAWINGS

Looking first at FIGS. I and II, therein is schematically illustrated atwo countershaft transmission 10 including four forward speed ratiogears and one reverse speed ratio gear. The transmission controlsdisclosed in the additional figures are designed to automatically effectpower shifting of the four forward speed ratios between the first andfourth speed ratios and to effect power shifting between the first andreverse speed ratios.

Transmission 10 includes an input shaft 12 which may be directly drivenby an unshown internal combustion engine; a housing assembly 14; atorque converter assembly 16; a ratio change gear assembly 18 driven byinput shaft 12 through torque converter assembly 16 in first, second,and reverse speed ratios and driven directly by a bypass input shaft 13in third and fourth speed ratios; and an output shaft 20 axially alignedwith input shaft 12.

The torque converter assembly 16 is conventional in that it includes afluid coupling of the torque converter type having an impeller 22adriven by input shaft 12 through a shroud 24, a turbine 22bhydraulically driven by the impeller and in turn driving a sleeve shaft26 extending into gear assembly 18, and a runner or stator 28 whichbecomes grounded to housing 14 via a one-way roller clutch 30 carried bya sleeve shaft 32 fixed to housing assembly 14. Shroud 24 also drives apump 34 for pressurizing the torque converter, for lubricating thetransmission, and for selectively actuating clutches in gear assembly 18via controls to be described hereinafter.

Sleeve 26 provides a fluid powered or torque converter driven shaft forfirst, second, and reverse ratio gears in gear assembly 18. Bypass shaft13 is in continuous direct drive with input shaft 12 and provides atorque converter bypass for driving third and fourth ratio gears; thisarrangement of the bypass shaft negates the need for a separate torqueconverter bypass clutch.

Looking now at FIGS. I and II, the schematically illustrated ratiochange gear assembly includes two power paths or countershaft assemblies36 and 38 disposed about axes parallel to and radially outward of anaxis defined by shafts 12, 13, and 20. Assembly 36 includes a shaft 40rotatably supported in unshown bearings at its ends 40a and 40b byhousing assembly 14, a double acting synchronizer-jaw clutch 42, firstand third speed ratio gears 44 and 46 rotatable relative to andsupported by shaft 40, and a hydraulically actuated friction clutch 48.First speed ratio gear 44 is driven by and in continuous mesh with aninput drive gear 50 which is nonrotatably secured to torque converterdriven shaft 26. Third speed ratio gear 46 is driven by and incontinuous mesh with an input drive gear 52 which is nonrotatablysecured to bypass shaft 13. Synchronizer-jaw clutch 42 may be a doubleacting synchronizer clutch such as shown in previously mentionedApplication Ser. No. 178,429 and now U.S. Pat. No. 4,375,171. Briefly,clutch 42 includes a clutch member 54 at one end which is nonrotatablysecured to gear 44, a clutch member 56 at the other end which isnonrotatably secured to gear 46, and a center clutch member 58 at thecenter which is nonrotatably secured to shaft 40. Center clutch member58 may be slidably shifted leftwardly or rightwardly in a conventionalmanner to respectively couple gear 44 or 46 to shaft 40. Such slidableshifting of the center clutch member frictionally couples countershaft40 with one of the ratio gears to effect synchronism and then positivelyclutches the shaft with the gear via a jaw clutch. Center clutch member58 includes a radially extending flange portion 60a gripped by anunshown shift fork to effect the leftward and rightward shifting in aconventional manner in response to movement of a piston in a 1-3 synchroactuator 61 shown in FIG. IV. Friction clutch 48 includes a housingmember 62 nonrotatably secured to shaft 40, two sets of interdigitateddisks 64 and 65, and a sleeve shaft 66 rotatably supported by shaft 40.Disks 64 are nonrotatably secured to sleeve shaft 66 and disks 65 arenonrotatably secured to housing member 62. Both disk sets are axiallymoveable in housing 62 and are frictionally interconnected in responseto hydraulic pressure being selectively applied to an unshown piston inthe housing member 62 via a line 69. Sleeve shaft 66 is nonrotatablysecured to a drive gear 68 which is rotatably supported by shaft 40.Drive gear 68 is in continuous mesh with an output gear 70 which isnonrotatably secured to output shaft 20.

Countershaft assembly 38 differs from assembly 36 mainly in that it alsoincludes a reverse ratio gear 80. Assembly 38 includes a shaft 72rotatably supported in unshown bearings at its ends 72a and 72b byhousing assembly 14, a double acting synchronizer-jaw clutch 74, second,fourth and reverse speed ratio gears 76, 78, 80 which are rotatablerelative to and supported by shaft 72, a hydraulically actuated frictionclutch 82, and a reverse synchronizer-jaw clutch 84. Second speed ratiogear 76 is driven by and in continuous mesh with an input drive gear 86which is nonrotatably secured to torque converter driven shaft 26.Fourth speed ratio gear 78 is driven by and in continuous mesh with theinput drive gear 52 which, as previously mentioned, is nonrotatablysecured to bypass shaft 13. Synchronizer-jaw clutch 74 is a doubleacting clutch and may be identical to synchronizer-jaw clutch 42.Synchronizer-jaw clutch 74 includes a clutch member 90 at one end whichis nonrotatably secured to gear 76, a clutch member 92 at the other endwhich is nonrotatably secured to gear 78, and a center clutch member 96at the center which is nonrotatably secured to shaft 72. Center clutchmember 96 may be slidably shifted leftwardly or rightwardly in aconventional manner to respectively couple gear 76 or 78 to shaft 72.Such slidable shifting of the center clutch member frictionally couplescountershaft 72 with one of the ratio gears to effect synchronism andthen positively clutches the countershaft with the gear via a jawclutch. Center clutch member 96 includes a radially extending flangeportion 96a gripped by an unshown shift fork to effect the leftward andrightward shifting in a conventional manner in response to movement of apiston in a 2-4 synchro actuator 97 shown in FIG. IV. Friction clutch 82may be identical to friction clutch 48. Friction clutch 82 includes ahousing member 98 which is nonrotatably secured to shaft 72, two sets ofdisks 100 and 101, and a sleeve shaft 102 rotatably supported by shaft72. Disks 100 are nonrotatably secured to sleeve shaft 102 and disks 101are nonrotatably secured to housing member 98. Both disk sets areaxially moveable in housing 98 and are frictionally interconnected inresponse to hydraulic pressure being selectively applied to an unshownpiston in housing member 98 via a line 103. Sleeve shaft 102 isnonrotatably secured to a drive gear 104 which is rotatably supported byshaft 72. Drive gear 104 is in continuous mesh with an output gear 106which is nonrotatably secured to output shaft 20.

Reverse gear 80 is rotatably supported by shaft 72 and is driven by anidler gear assembly 108, seen only in FIG. II. Idler gear assembly 108includes a shaft 110 nonrotatably supported by housing assembly 14, agear 112 rotatably supported on shaft 110 and in continuous mesh withthe input drive gear 50 driven by torque converter driven shaft 26, anda gear 114 rotatably supported on shaft 110 and nonrotatably secured togear 112. Gear 114 is in continuous mesh with reverse gear 80.Synchronizer-jaw clutch 84 may be a single acting synchronizer clutchsuch as shown in previously mentioned U.S. Pat. No. 4,246,993. Briefly,clutch 84 includes a clutch member 116 secured to gear 80 and a clutchmember 118 nonrotatably secured to shaft 72. Member 118 may be slidablyshifted leftwardly in a conventional manner to couple gear 80 to shaft72. Such slidable shifting of member 118 frictionally couplescountershaft 72 with gear 80 to effect synchronism and then positivelyclutches the shaft with the gear via a jaw clutch. Member 118 includes aradially extending flange portion 118a gripped by an unshown shift forkto effect leftward and rightward shifting in a conventional manner inresponse to movement of a piston in a reverse synchro actuator 116 shownin FIG. IV.

By way of example, the ratios of ratio change gear assembly 18 are:first gear--4.05, second gear--2.22, third gear--1.42, fourthgear--1.00, and reverse gear--4.76.

From the foregoing one should note that only one speed ratio gear can beclutched to each countershaft at a given time and that the transmissionis input synchronized through the synchronizer-jaw clutches, that is,synchronizing power for the countershafts comes from the torqueconverter driven shaft for the first, second, and reverse speed ratios,and from the bypass shaft for the third and fourth speed ratios. Whiledrive through the transmission is via one countershaft, a ratio gear onthe other countershaft is synchronized and jaw clutched thereto; thetransmission may then be power shifted from one speed ratio gear orcountershaft by simultaneously disengaging one of the multiple disk,friction clutches 48 or 82 and engaging the other.

The transmission of FIGS. I and II may be broadly defined as apreselect, powershift transmission including a plurality of multipleratio gear (44, 46, 76, 78, 80) power paths (36, 38) alternatelyconnectable between input (12) and output (20) shafts by first engaging(preselecting) selected ones of clutch means (42, 74, 84) associatedwith each gear and then alternately engaging a powershift clutch (48,82) associated with each path.

Controls for automatically power shifting the transmission include ahydraulic logic system 118 shown in FIG. III and a hydraulic shift valvesystem 119, shown in FIG. IV. Shift valve system 119, which alsoincludes some logic functions, is discussed separately from hydrauliclogic system 118 since the shift valve system is readily interfaced withan electrical or electronic logic system in lieu of the hydraulic logicsystem and therefore may be considered separate and distinct.

In the following description of the controls, the material or structuredefining the valve bores and the passages interconnecting the bores isnot shown to simplify the drawings.

HYDRAULIC LOGIC SYSTEM 118

Looking first at the hydraulic logic system 118 in FIG. III, therein isa pressure regulator 120; a shift selector means or manual valve 112;forward speed shift valves designated 1-2 shift valve 124, 2-3 shiftvalve 126, and 3-4 shift valve 128; a 1-2 clutch shuttle valve 130; areverse sequence valve 132; a reverse timer valve 134; a synchro shuttlevalve 136; and a synchro shift valve 138.

Manual valve 122 is controlled by a vehicle operator. Shift valves 124,126, and 128 initiate alternate automatic power shifting of frictionclutches 48 and 82 in response to vehicle speed and throttle position.Shuttle valve 130 alternately effects engagement and disengagement offriction clutches 48 and 82 in response to position of the shift valves.Reverse sequence valve 132, reverse timer valve 134, synchro shuttle136, and a restriction 268 cooperate to sequence disengagement orneutral positioning of synchronizer-jaw clutch 74 prior to engagement ofreverse synchronizer-jaw clutch 84, to delay engagement of frictionclutch 82 during the sequencing, and to hold reverse synchronizer-jawclutch 84 engaged to allow power shifting between the first and reversespeed ratios when the vehicle speed is below a predetermined amount.Synchro shift valve 138 initiates automatic sequential engagement of theforward speed ratios in response to vehicle speed and in cooperationwith the position of valves 124 and 136.

PRESSURE REGULATOR VALVE 120

Regulator 120 receives a source of pressurized hydraulic oil via line140 from pump 34 and regulates the fluid at a reduced pressure in a line142. Regulator 120 includes a bore 144 blind at its lower end and havingannular parts 120a-120d, a spool or valving member 146 having lands146a-146c, and a spring 148 biasing the spool downward and reactingagainst a vented stop 150 which exhausts the space containing spring148. The blind end of bore 144 and stop 150 limit travel of the spool.Port 120a communicates with the source of pressurized hydraulic oil viathe line 140. Line 142 in turn communicates regulated pressure from port120b directly with port 120d via a branch line 142a and a restriction152. Line 142 also communicates the regulated pressure with an annularport 128a of 3-4 shift valve 128 via a branch line 142b, with a port124a of 1-2 shift valve 124 via a branch line 142c, with annular ports122a and 122b of manual valve 122 via branch lines 142d and 142e, withan annular port 132a of reverse sequence valve 132 via a branch line142f, and with an annular port 138a of synchro shift valve 138 via abranch line 142g. Port 120c communicates with an exhaust 154.

The force of spring 148 and the counter force of the hydraulic pressureacting on the bottom of spool 146 varies the amount of communicationbetween ports 120a and 120b via the annular space between lands 146a and146b to regulate the hydraulic pressure in line 142 at the desiredamount, for example 40-50 psi (2.8-3.5 kgm/sq.cm). Any excess pressurein line 142 moves land 146c upward enough to intercommunicate ports 120band 120c and vent the excess pressure to exhaust 154. Restriction 152dampens pressure surges which could cause flutter of spool 146.

Manual Valve 122

Valve 122 includes a bore 156 open to exhaust at both ends and havingannular ports 122a-122i, and a spool 158 having lands 158a-158e. Adrilled passage 158f in the spool communicates the space between lands158b and 158c to exhaust. The lower end of spool 158 is adapted in aconventional manner to be connected via an unshown linkage to an unshownshift selector controlled by a vehicle operator. However, spool 158could be controlled by some other means. Spool 158 is incrementallymoveable downward by the shift selector from a reverse drive position,as shown, to a neutral position; to a forward drive position for normalautomatic upshift and downshift between first and fourth; to an inhibitor third speed ratio position for normal automatic upshift and downshiftbetween first and third with inhibited automatic shifts into and out offourth; to a second speed ratio position for normal automatic upshiftand downshift between first and second with inhibited automatic shiftsinto and out of third and fourth; and to a first speed ratio positionfor normal first speed operation and inhibited automatic shifts into andout of second, third, and fourth.

Looking at ports 122a-122i from top to bottom, port 122c communicatesvia a line 160 with an annular port 124b of 1-2 shift valve 124. Port122c also communicates via a reverse signal line 162 with an annularport 134a of reverse timer valve 134 and via a branch line 162a with anannular port 132b of reverse sequence valve 132. Port 122a communicatesdirectly with regulated pressure in branch line 142d. Port 122dcommunicates via a line 164 with an annular port 128b of 3-4 shift valve128. Port 122e communicates via a line 166 with an annular port 126a of2-3 shift valve. Port 122f communicates via a line 168 with an annular124c of 1-2 shift valve 124. Port 122b communicates directly withregulated pressure in branch line 142e. Ports 122g and 122h communicatein parallel via a line 170 with an annular port 130a of 1-2 clutchshuttle valve 130. And port 122i communicates via a line 172 with anannular port 134b of reverse timer 134 and via a branch line 172a withan annular port 132c of reverse sequence valve 132.

With spool 158 in the reverse position, as shown, the annular spacebetween lands 158a and 158b communicates regulated pressure from port122a to port 122c which in turn communicates via lines 160, 162 and 162awith ports 124b, 134a, and 132b. Also the space between lands 158d and158e communicates port 122h with port 122i, which ports in turnrespectively communicate via line 170 with port 130a and via lines 172and 172a with ports 134b and 132c. Further, port 122d communicates viadrilled passage 158f with exhaust. All other ports are blocked fromintercommunication by the lands.

With spool 158 in the neutral position, land 158a is below port 122c,thereby exposing port 122c directly to exhaust, and land 158e isdisposed below the lower end of bore 156, thereby exposing ports 122hand 122i to exhaust via the space between lands 158d and 158e. Ports122d and 122e communicate via drilled passage 158f with exhaust. Allother ports are blocked from intercommunication by the lands.

With spool 158 in the forward drive position, ports 122c, 122d, 122e,and 122i continue to communicate with exhaust. Additionally, port 122fcommunicates with exhaust via drilled passage 158f and land 158d nowblocks port 122h. Further, the space between lands 158c and 158dcommunicates regulated pressure from port 122b to port 122g. With spool158 in the drive position the logic system and shift valve system maythen effect automatic upshifts and downshifts in the four forward speedsas a function of vehicle speed and throttle position.

With spool 158 in the third speed ratio position, ports 122c, 122e,122f, and 122i continue to communicate with exhaust, port 122h remainsblocked by land 158d, and port 122b continues to communicate with port122g. However, port 122d is now blocked from exhaust by land 158b and isnow communicated with regulated pressure at port 122a via the spacebetween lands 158a and 158b. Hence, regulated pressure now flows to port128b of 3-4 shift valve 128 via line 164 to raise the shift point ofvalve 128 and thereby inhibit automatic shifts into and out of thefourth speed in a manner to be explained hereinafter.

With spool 158 in the second speed ratio position, ports 122c, 122f, and122i continue to communicate with exhaust. The space between lands 158cand 158d now communicates regulated pressure to both ports 122g and 122hwith no change in fluid flow since line 170 is connected to both ports.However, port 122e is now blocked from exhaust by land 158b along withport 122d. Hence, regulated pressure also flows to port 126a of 2-3shift valve 126 via line 166 to also raise the shift point of valve 126and thereby inhibit automatic shifts into and out of both the third andfourth speed ratios in a manner explained hereinafter.

With spool 158 in the first speed ratio position, only port 122ccontinues to communicate with exhaust, port 122i is blocked by land158d, and the space between lands 158c and 158d continues tointercommunicate ports 122b, 122g, and 122h. However, port 122f is nowblocked from exhaust by land 158b along with ports 122d and 122e. Hence,regulated pressure also flows to port 124c of 1-2 shift valve 124 vialine 168 to also raise the shift point of valve 124 and thereby inhibitautomatic shifts into and out of the second, third, and fourth speedratios in a manner explained hereinafter.

1-2 Shift Valve 124

Valve 124, which is shown enlarged in FIG. III-A, includes a steppedbore 174 having axially aligned bore portions 174a-174c of successivelyincreasing diameter and annular ports 124a-124h, and a stepped spool 176biased downward by a spring 178 which reacts against an annular ordoughnut-shaped inhibit piston 180 slidably disposed in bore portion174c. In FIG. III-A spool 176 is actuated up and piston 180 is actuateddown to illustrate, respectively, the second speed ratio position ofspool 176 and the inhibit position of piston 180. The bottom of boreportion 174a is blind and the top of bore portion 174c is sealed by aplug 182 having a downwardly projecting stop portion 182a slidablyreceived by the opening in annular piston 180. The space containingspring 178 is vented by an exhaust 184. Spool 176 includes from bottomto top lands 176a-176c of equal diameter and a land 176d of greaterdiameter. Port 124c communicates directly with a space between piston180 and plug 182. Port 124d continuously communicates with a throttlemodulation pressure via a line 186, an annular port 126b, a line 188, anannular port 128c, and a line 190 which receives hydraulic pressureinversely proportional to throttle position or manifold pressure via aconventional modulator valve 192. Port 124b, as previously mentioned,communicates with port 122c of the manual valve via line 160 andreceives regulated pressure only when the manual valve spool 158 is inthe reverse position. Ports 124e and 124f communicate in parallel via aY-line 194 with an annular port 126c. Port 124a is connected directly toregulated pressure in branch line 142c. Port 124g is connected via aline 196 to an annular port 138b of synchro shift valve 138. Port 124hcontinuously communicates via a line 198 with a hydraulic governorpressure which increases in proportion to vehicle speed and which isproduced by a governor valve 200 in a conventional manner.

Spool 176 is basically a two position valving member. When the downwardforce of spring 178 acting on spool 176 exceeds the upward force of thegovernor pressure acting on the bottom area of the spool plus the upwardforce of the modulator pressure acting on the spool shoulder formed bythe difference in diameter of lands 176c and 176d, spool 176 will be inthe downward or first speed ratio position. As the combined upwardforces from the governor and modulator pressures increase in response tovehicle speed and throttle position, spool 176 will shift upward towardstop 182a to effect a 1-2 upshift into the second speed ratio position.Conversely, the spool shifts downward to effect a 2-1 downshift as thecombined governor and modulator pressures decrease.

When manual valve 122 ports regulated pressure to port 124c via line168, piston 180 moves downward against the shoulder formed by thedifference in diameter of bore portions 174c and 174b, therebyincreasing the biasing force of spring 178 on spool 176 and raising orinhibiting the shift point of spool 176 for a given combination ofgovernor and modulator pressures. Since the rate of spring 178 and thestroke of piston 180 may be accurately controlled, the up-and-down shiftpoints of spool 176 are also accurately controlled without concern orneed to control the hydraulic pressure used to raise or inhibit theshift points.

2-3 Shift Valve 126

Valve 126 is much like valve 124 and is also shown enlarged in FIG.III-A. The valve includes a stepped bore 202 having bore portions202a-202c of successively increasing diameter and annular ports126a-126f, and a stepped spool 204 biased downward by a spring 206 whichreacts against an annular or doughnut-shaped inhibit piston 208 slidablydisposed in bore portion 202c. The bottom of bore portion 202a is blindand the top of bore portion 202c is sealed by a plug 210 having adownwardly projecting stop portion 210a fixed thereto and slidablyreceived by the doughnut opening in piston 208. The space containingspring 206 is vented by an exhaust 212. Spool 204 includes from bottomto top lands 204a-204c of equal diameter and a land 204d of greaterdiameter. Port 126a communicates directly with a space between piston208 and plug 210. As previously mentioned, port 126b continuouslycommunicates with hydraulic pressure inversely proportional to throttleposition (modulator pressure) and port 126c communicates with ports 124eand 124f via line 194. Port 126d communicates via a line 214 with a port128d of 3-4 shift valve 128. Port 126e vents the space between lands204a and 204b to an exhaust 216. Port 126f continuously communicates viaa branch line 198a with the governor pressure proportional to vehiclespeed.

The operation of valve 126 is substantially the same as valve 124. Spool124 is shifted from its downward or second speed ratio position to itsupward or third speed position merely by a higher combination ofgovernor and modulator pressures. Piston 208 is shifted downward againstthe shoulder defined by the difference in diameter between bore portions202b and 202c in response to regulated pressure (i.e., an inhibitsignal) at port 126a via line 166.

3-4 Shift Valve 128

Valve 128 is much like valves 124 and 126 and is also shown enlarged inFIG. III-A. The valve includes a stepped bore 218 having bore portions218a-218d of successively increasing diameter and annular ports128a-128f, and a stepped spool biased downward by a spring 222 whichreacts against an annular or doughnut-shaped inhibit piston 224 slidablydisposed in bore portion 218d. The bottom of bore portion 218a is blindand the top of bore portion 218d is sealed by a plug 226 having adownwardly projecting stop portion 226a fixed thereto and slidablyreceived by the doughnut opening in piston 224. The space containingspring 222 is vented by an exhaust 227. Spool 220 includes, from bottomto top, lands 220a-220c of equal diameter and a land 220d of greaterdiameter. Port 128b communicates directly with a space between piston224 and plug 226 and receives regulated pressure only when the manualvalve spool 158 is in the third speed ratio position. As previouslymentioned, port 128c continuously communicates with hydraulic modulatorpressure inversely proportional to throttle position, port 128acontinuously communicates with regulated pressure via branch line 142b,and port 128d communicates with port 126d via line 214. Port 128ecommunicates via a line 228 with an annular port 130b of 1-2 clutchshuttle valve 130. Port 128f continuously communicates via a branch line198b with governor pressure proportional to vehicle speed. A nonannularport 128g on the left side of bore portion 218a communicates via a line230 with an annular port 130c of 1-2 clutch shuttle valve 130. Anonannular port 128h, diametrically opposite port 128g, is connected toan exhaust 232 via a restriction 234.

Operation of valve 128 is substantially the same as valves 124 and 126;spool 220 is shifted from its downward or third speed ratio position toits upward or fourth speed ratio position merely by a higher combinationof modulator and governor pressures. Piston 224 is shifted downwardagainst the shoulder defined by the difference in diameter between boreportions 218c and 218d in response to regulated pressure (i.e., aninhibit signal) at port 128b via line 164.

1-2 Clutch Shuttle Valve 130

Valve 130 includes a straight bore 236 blind at its lower end and havingannular ports 130a-130f, a spool 238 having lands 238a-238c, and aspring 240 biasing the spool downward and reacting against a vented stop242 which exhausts the space containing spring 240. As previouslymentioned, port 130c communicates via a line 230 with a port 128g of 3-4shift valve 128, port 130a communicates via a line 170 with ports 122gand 122h, and port 130b communicates via line 228 with port 128e of 3-4shift valve 128. Port 130c also communicates with an exhaust 244 via arestriction 246. Port 130d communicates via a line 248 with a clutch 48selector valve in the hydraulic shift valve system to be describedhereinafter. Port 130e communicates via a line 150 with a clutch 82selector valve in the hydraulic shift valve system, also to be describedhereinafter. For now is should suffice to say that the presence ofhydraulic pressure in either line 248 or 250 initiates an action in theshift valve system to effect a controlled engagement of the respectivefriction clutch 48 or 82, provided one of corresponding ratio gears hasbeen synchronized and jaw clutched to the countershaft of the frictionclutch to be engaged. Further, the absence of hydraulic pressure ineither line 248 or 250 initiates a controlled disengagement of therespective friction clutch. Port 130f communicates with an exhaust 252via a restriction 254.

Restrictions 234 and 246, associated respectively with valves 128 and130, control the disengagement rate of clutch 48 during 1-2 upshifts and3-2 downshifts. During 3-4 upshifts spool 220 of 3-4 shift valve 128 isup, whereby land 220a blocks communication between ports 128g and 128h.Hence, only restriction 246 controls the disengagement rate of clutch 48during 3-4 upshifts. Restriction 254 controls the disengagement rate ofclutch 82 during 2-1 and 4-3 downshifts and during 2-4 upshifts.

In a manner more fully explained hereinafter, the downward position ofspool 238 communicates line 248 with line 170 via port 130d, the spacebetween lands 238b and 238c, and port 130a, whereby regulated pressureflows to line 248 when spool 158 of manual valve 122 is in the drive,third, second, or first speed ratio positions and when spool 158 is inthe reverse position provided the, as yet unexplained, reverse timervalve 134 is timed out, i.e., the spool therein is actuated to its upposition. The down position of spool 238 also communicates line 250 withexhaust 252 via port 130e, the space between lands 238a and 238b, port130f, and restriction 254. The up position of spool 238 communicatesline 250 with line 170 via port 130e, the space between lands 238a and238b, and port 130a, whereby regulated pressure flows to line 250 whenspool 158 is in the as mentioned position. The up position of spool 238also communicates line 248 with exhaust 244 via port 130d, the spacebetween lands 238b and 238c, port 130c, and restriction 246; when spool220 of 3-4 shift valve 128 is down line 248 also vents to exhaust 232via restriction 234 in parallel with restriction 246, as exlained in thepreceeding paragraph.

In a manner more fully explained hereinafter, shift valves 124, 126, and128 block the flow of hydraulic pressure to shift spool 238 upward whenline 250 is to be depressurized and line 248 is to be pressurized forshifts into the first and third speed ratios. Shift valves 124, 126, and128 allow the flow of hydraulic pressure to shift spool 238 upward whenline 248 is to be depressurized and line 250 is to be pressurized forshifts into reverse, second, and fourth.

Reverse Sequence Valve 132

Valve 132, which is shown enlarged in FIG. III-B, includes a steppedbore 256 blind at its lower end and having bore portions 256a-256c ofsuccessively increasing diameter and annular ports 132a-132e, a steppedspool 258 having lands 258a-258c of successively increasing diameter,and a spring 260 biasing spool 258 downward and reacting against a plug262 which seals the top of the bore. The space containing spring 260continuously communicates via a branch line 198c with the governorpressure proportional to vehicle speed. As previously mentioned, port132a continuously communicates with regulated pressure via branch line142f of line 142, port 132b communicates with port 122c via branch line162a of line 162, and the port 132c communicates via branch line 172a ofline 172 with port 122i of manual valve 122. Port 132d communicates viaa line 264 with an annular port 134c of reverse timer valve 134 througha restriction 266, with an annular port 136a of synchro shuttle valve136, and with a reverse on/off selector valve through a restriction 268.The reverse on/off selector valve forms part of the hydraulic shiftvalve system to be described hereinafter. For now it should suffice tosay that the presence of hydraulic pressure in line 264 initiatesengagement of reverse synchronizer-jaw clutch 84 and that the absence ofhydraulic pressure initiates disengagement of the reversesynchronizer-jaw clutch. Port 132e communicates with an exhaust 269.

The down-and-up positions of spool 258 correspond respectively todisengagement and engagement states of valve 132 and in turn correspondrespectively to the disengaged and engaged positions of the reversespeed ratio. As previously mentioned, spool 258 is continuously biaseddownward by spring 260 and governor pressure which varies with vehiclespeed. When manual valve spool 158 is placed in the reverse position,regulated pressure (via port 122c) acts upward on a first shoulderdefined by the difference in diameter of lands 258a and 258b. The upwardforce of the regulated pressure acting on this first shoulder issufficient to shift the spool to its full up position when the downwardforce of the governor pressure is proportional to a predeterminedamount, e.g., approximately 3 miles per hour (4.8 kilometers per hour).With spool 258 in the up position, as shown in FIG. III-B, regulatedpressure at port 132a is communicated via the space between lands 258band 258c and port 132d to line 264 to initiate a reverse speed ratioengagement sequence. Further, the regulated pressure acts on a secondshoulder defined by the difference in diameter of lands 258b and 258c.The upward force of the regulated pressure acting on this secondshoulder is sufficient, independent of the upward force from the firstshoulder, to latch the spool in the up position when the governorpressure is proportional to approximately 6 miles per hour (9.6kilometers per hour). Hence, once valve spool 258 is moved up or to theengagement state, it will remain up independent of changes in theposition of manual valve spool 158 for vehicle speed less than 6 milesper hour. In a manner to be explained in greater detail hereinafter, thelatched position of spool 258 facilitates power shifting thetransmission between the first and reverse speed ratios when manualvalve spool 158 is moved between reverse and drive to effect a rockingmotion of the vehicle.

Reverse Time Valve 134

Valve 134, which is also shown enlarged in FIG. III-B, includes astepped bore 270 having bore portions 270a-270b and annular ports134a-134c, a piston 272 having an extension 272a, an open centered spool274 allowing passage of piston extension 272a and having lands274a-274b, a spring 276 reacting between piston 272 and spool 274, aspring 278 reacting between spool 274 and an open centered stop 280having a cylindrical extension portion 280a which limits upward movementof spool 274. Bore 270 is blind at its lower end and the spacescontaining springs 276 and 278 are vented by the open center of stop280. As previously mentioned annular port 134b communicates via line 172with annular port 122i of manual valve 122 and with port 132c via branchline 172a, port 134a communicates via line 162 with port 122c and withport 132b via branch line 162a, and port 134c communicates throughrestriction 266 with port 132d via line 264.

Also, as previously mentioned, when the spool of reverse sequence valve132 is shifted upward, in response to initial movement of manual valvespool 158 to the reverse position while the vehicle speed is less than 3miles per hour, hydraulic pressure flows to line 264. The pressure inline 264 flows to port 134c via restriction 266 at a controlled rate andmoves piston 272 up at a timed rate. After a predetermined time or delaythe increasing force of spring 276 shifts spool 274 up, as shown in FIG.III-B, to communicate port 134a with port 134b via the space betweenlands 274a and a 274b, whereby hydraulic pressure at port 134a flows vialine 172 and branch line 172a to port 132c of reverse sequence valve 132to additionally latch spool 258 upward against governor pressuresrepresentive of vehicle speeds in the range of 18 miles per hour (28.9kilometers per hour). The regulated pressure in line 172 also flows toport 122i of the manual valve and on through shuttle valve 130 toinitiate engagement of powershift, friction clutch 82 in a mannerpreviously mentioned. Should manual valve spool 158 move from thereverse position during vehicle speeds less than 6 miles per hour,reverse sequence valve spool 258 will remain in the latched or upposition. Hence, the regulated pressure in line 264 will maintain spool274 in the up position.

Synchro Shuttle Valve 136

Valve 136, which is also shown enlarged in FIG. III-B, includes astraight bore 282 blind at its lower end and having annular ports136a-136d, a spool 284 having lands 248a-284b, and a spring 286 biasingthe spool downward and reacting against an open centered stop 288 whichvents the space containing spring 286 to exhaust. As previouslymentioned, port 136a communicates with port 132d of reverse sequencevalve 132 via line 264. Port 136b communicates via a line 290 with port136c which in turn continuously communicates via a line 292 with a 2-4synchro selector valve in the hydraulic shift valve system to bedescribed hereinafter. For now it should suffice to say that the absenceof hydraulic pressure in line 292 initiates engagement of the secondspeed ratio portion of synchronizer-jaw clutch 74 and that the presenceof hydraulic pressure in line 292 initiates engagement of the fourthspeed ratio portion of synchronizer-jaw clutch 74. Port 136dcommunicates via a line 294 with a port 138c of synchro shift valve 138.The presence of hydraulic pressure in line 264 shifts spool 284 upagainst stop 288, as shown in FIG. III-B, whereby land 284a uncoversport 136b to allow the flow of hydraulic pressure to line 292 via ports136a and 136b, line 290, and port 136c. In the up position of spool 284,land 284a blocks port 136d.

Synchro Shift Valve 138

Valve 138, which is also shown enlarged in FIG. III-B, includes astepped bore 296 having bore portions 296a-296b of successivelyincreasing diameter, annular ports 138a-138e, a stepped spool 298 havinglands 298a-298b of equal diameter and a land 298c of greater diameter,and a spring 300 biasing the spool downward and reacting against an opencentered stop 302 which exhausts the space containing spring 300 andlimits upward movement of spool 298. As previously mentioned port 138acommunicates directly with regulated pressure via branch line 142g andline 142, port 138b communicates via line 196 with port 124g of 1-2shift valve 124, and port 138c communicates via line 294 with port 136dof synchro shuttle valve 136. Port 138d communicates via a line 304 witha 1-3 synchro selector valve in the hydraulic shift valve system to bedescribed hereinafter. For now it should suffice to say that the absenceof hydraulic pressure in line 304 initiates engagement of the firstspeed ratio portion of synchronizer-jaw clutch 42 and that the presenceof hydraulic pressure in line 304 initiates engagement of the thirdspeed ratio portion of synchronizer clutch 42. Port 138e is connected toan exhaust 306.

OPERATION OF HYDRAULIC LOGIC SYSTEM 118

Looking now briefly at valves 136 and 138, spool 298 of valve 138 isprogressively moved upward in response to increasing governor pressuresupplied to the bottom of the spool via port 138b, line 196, port 124g,and port 124h when spool 176 of 1-2 shift valve 124 is up. For vehiclespeeds below the 1-2 shift point of valve 124, land 176a of 1-2 shiftvalve 124 blocks the flow of governor pressure to the bottom of spool298. Hence, spool 298 is in the down position shown and land 298b blocksthe flow of regulated hydraulic pressure from port 138a to ports 138dand 138c, whereby there is no hydraulic pressure in lines 292 and 304unless spool 284 of shuttle valve 136 is up. When spools 284 and 298 aredown the absence of pressure in lines 292 and 304 is ensured since bothlines are vented to exhaust 306, whereby the shift valve system 119initiates engagement of both the first and second speed ratio portionsof synchronizer-jaw clutches 42 and 74 regardless of the position ofspool 158 in manual valve 122.

When spool 158 of manual valve 122 is placed in any of the forward drivepositions, the space between lands 158c and 158d communicates regulatedpressure to ports 122g and 122h and on to line 248 to initiateengagement of clutch 48 via line 170, port 130a, the space between lands238b and 238c, port 130d, line 248 and yet undescribed valving in shiftvalve system 119. As vehicle or the transmission output speed increases,spool 176 of 1-2 shift valve 124 moves up and allows the flow ofgovernor pressure to the bottom of spool 298 of synchro shift valve 138to start upward movement of the spool. As the governor pressureincreases in response to a further increase in vehicle speed, land 298amoves to a position, see FIG. III-B, communicating regulated pressurefrom port 138a to port 138d via the space between lands 298a and 298bprior to a 2-3 upshift of 2-3 shift valve spool 204, therebyanticipating a 2-3 upshift to initiate disengagement of the first speedratio portion of synchronizer-jaw clutch 42 and to initiate (i.e.,preselect) engagement of the third speed ratio portion ofsynchronizer-jaw clutch 42 prior to the 2-3 upshift of valve 126. Whenspool 204 of valve 126 upshifts, land 204b of spool 204 will block theflow of regulated pressure to the bottom of spool 238 of 1-2 clutchshuttle valve 130 via port 126c, line 214, port 128d, the space betweenlands 220b and 220c, port 128e, line 228, and port 130b. At the sametime the space between lands 204a and 204b communicates this same seriesof ports and lines to exhaust 216 to faciliate a quick down shuttle ofspool 238 and therefore a flow of regulated pressure to line 248 toinitiate engagement of clutch 48 via valving in shift valve system 119for the 2-3 upshift.

As the governor pressure further increases in response to a continuedincrease in vehicle speed, land 298b further moves to a position whereinthe space between lands 298a and 298b also communicates regulatedpressure to port 138c and on to line 292 via the previously describedpath prior to a 3-4 upshift of valve spool 220 in 3-4 shift valve 128,thereby anticipating a 3-4 upshift to initiate disengagement of thesecond speed ratio portion of synchronizer-jaw clutch 74 and to initiate(i.e., preselect) engagement of the fourth speed ratio portion ofsynchronizer-jaw clutch 74 prior to a 3-4 upshift of valve 128. Whenspool 220 of valve 128 upshifts, land 220b blocks port 128d to isolatethe path to exhaust 216 for line 228 and land 220c unblocks port 128a tocommunicate regulated pressure to upshift shuttle valve spool 238 viathe space between lands 220b and 220c, port 128e, line 228, and port130b. Downshifting is basically the reverse of upshifting.

When the spool 158 of manual valve 122 is placed in the reverseposition, regulated pressure immediately flows to the bottom of shuttlevalve spool 238, to port 132b of reverse sequence valve 132, and to port134a of reverse timer valve 134. The flow path to the bottom of shuttlevalve spool 238 is via port 122c, line 160, port 124b, the space betweenlands 176b and 176c, port 124e, line 194, port 126c, the space betweenlands 204b and 204c, port 126d, line 214, port 128d, the space betweenlands 220b and 220c, port 128e, line 228, and port 130b; this path, ofcourse, is blocked if spool 176 is up. The flow path to port 132b ofreverse sequence valve 132 and port 134a of reverse timer valve 134 isvia port 122c, line 162, and branch line 162a. The flow of regulatedpressure to line 250 is delayed by reverse timer valve 134 to allowdisengagement of the second and fourth speed ratio jaw clutch portionsof synchronizer-jaw clutch 74 and engagement of reverse synchronizer-jaw84 clutch. The regulated pressure on port 132b acts on the firstshoulder of spool 258 and shifts the spool up if vehicle speed is lessthan the previously mentioned 3 miles per hour. When spool 258 shiftsup, regulated pressure flows to line 264 to start the timed movement ofpiston 272 of reverse timer valve 234, to upshift of spool 284 ofshuttle valve 136 for allowing the flow of regulated pressure to line292 and for blocking the flow of regulated pressure to line 294, and toinitiate engagement of the reverse synchronizer-jaw clutch throughrestriction 268 which delays engagement of the reverse synchronizer-jawclutch. The regulated pressure in both lines 292 and 264 is used tocenter or neutrally position the three position piston in 2-4 synchroactuator 97 in a manner to be described hereinafter. When reverse timer134 times out spool 274 upshifts and communicates regulated pressure onport 134a to line 250 to initiate engagement of powershift clutch 82.The flow path from port 134a to line 250 is via the space between lands274a and 274b, port 134b, line 172, port 122i, the space between lands158e and 158d, port 122h, line 170, and on to line 250, as previouslydescribed.

HYDRAULIC SHIFT VALVE SYSTEM 119

Looking now at shift valve system 119 of FIG. IV, therein is shown inaddition to the shift valves, the previously mentioned 1-3 synchroactuator 61, 2-4 synchro actuator 97, and reverse synchro actuator 116.

The 1-3 synchro actuator 61, as previously mentioned, is a two position,piston type actuator. The actuator includes a housing 314 defining astepped through bore having bore portions 316a-316c of successivelydecreasing diameter, an end plate 318 disposed in bore portion 316a andclosing the right end of the bore, and a piston 320 slidably disposed inbore portion 316b and fixed or formed with a rod 322 slidably extendingat one end through an opening in plate 318 and at the other end throughbore portion 316c. The left end of rod 322 is fixed to a partially shownshift fork 324 which engages flange portion 60a of 1-3 synchronizer-jawclutch 42 in a conventional manner. Ports 314a and 314b provide passagesin the housing for directing hydraulic oil to and from opposite sides ofpiston 320.

When piston 320 is fully left in bore portion 316b, as shown, firstspeed ratio gear 44 is coupled to countershaft 40 by an unshown jawclutch portion in clutch 42 and gear 46 is free to rotate relative tocountershaft 40. When piston 320 is moved from left to right the jawclutch portion coupling gear 44 to countershaft 40 disengages, thesynchronizer and blocker portion of clutch 42 then frictionally couplesthe countershaft to third speed ratio gear 46 and blocks furtherrightward movement of piston 320 until gear 46 and countershaft 40 reachsynchronism. When synchronism is reached, the blocker portion of clutch42 unblocks and allows full rightward movement of piston 320, wherebythe unshown jaw clutch portion engages to effect a positive couplingbetween third speed ratio gear 46 and countershaft 40. The first speedratio gear 44 is synchronized and jaw clutched to countershaft 40 in thesame manner in response to movement of piston 320 from right to left.Piston 320 is either full left or right.

The 2-4 synchro actuator 97, as previously mentioned, is a threeposition, piston type actuator. The actuator includes a housing 326defining a stepped through bore having bore portions 328a-328d ofsuccessively decreasing diameter, an end plate 330 closing the right endof the bore, and a piston assembly including a piston 332 fixed orformed with a rod 334 and a piston 336 slidably disposed on rod 334.Pistons 332 and 336 are respectively disposed for sliding movement inbore portions 328c and 328b. Piston 336 includes an axially extendingsleeve or stop ring portion 336a which limits leftward movement ofpiston 332 and moves piston 332 to the neutral position, as shown, whenpiston 336 abuts the shoulder defined by the difference in diameter ofbore portions 328b and 328c. Rod 334 slidably extends at one end throughan opening in plate 330 and at the other end through bore portion 328d.The left end of rod 334 is fixed to a partially shown shift fork 338which engages flange portion 96a of 2-4 synchronizer-jaw clutch 74 in aconventional manner. Ports 326a-326c provide passages in housing 326 fordirecting hydraulic oil to and from opposite sides of pistons 332 and336.

When piston 332 is in the neutral or center position, as shown,synchronizer-jaw clutch 74 is in neutral, whereby second and fourthspeed ratio gears 76 and 78 are free to rotate relative to countershaft72. When piston 332 is moved toward the left end of bore portion 328c,the synchronizer and blocker portion of clutch 74 frictionally couplescountershaft 72 to second speed ratio gear 76 and blocks furtherleftward movement of piston 332 until gear 76 and countershaft 72 reachsynchronism. When synchronism is reached, the blocker portion of clutch74 unblocks and allows full leftward movement of piston 332 in boreportion 328c, whereby the unshown jaw clutch portion engages to effect apositive coupling between second speed ratio gear 76 and countershaft72. The fourth speed ratio gear 78 is synchronized and jaw clutched tocountershaft 72 in the same manner in response to movement of piston 332rightwardly in bore portion 328c. To insure a neutral position of piston332 pressurized oil is simultaneously communicated to ports 326a and326c in a manner described hereinafter.

The reverse synchro actuator 116, as previously mentioned, is a twoposition piston type actuator. The actuator includes a housing 340defining a stepped through bore having bore portions 342a-342c ofsuccessively decreasing diameter, an end plate 344 closing the right endof the bore, and a piston 346 slidably disposed in bore portion 342b andfixed or formed with a rod 348 slidably extending at one end through anopening in plate 344 and at the other end through bore portion 342c. Theleft end of rod 348 is fixed to a partially shown shift fork 350 whichengages flange portion 118a of reverse synchronizer-jaw clutch 84 in aconventional manner. Ports 340a and 340b provide passages in the housingfor directing hydraulic oil to and from opposite sides of piston 346.

When piston 346 is fully right in bore portion 342b, as shown, reversespeed ratio gear 80 is free to rotate relative to countershaft 72. Whenpressurized oil is communicated to the right side of piston 346 via port340b, piston 346 moves leftwardly and the unshown synchronizer andblocker portions of clutch 84 frictionally couple countershaft 72 toreverse speed ratio gear 80 and block further leftward movement ofpiston 346 until gear 80 and countershaft 72 reach synchronism. Whensynchronism is reached, the blocker portion of clutch 84 unblocks andallows full leftward movement of the piston in bore portion 342b,whereby an unshown jaw clutch engages to effect a positive couplingbetween gear 80 and countershaft 72. When piston 396 is moved from leftto right, the jaw clutch portion disengages gear 80. Hydraulic sealingof all three actuators is provided in a conventional manner.

Looking now specifically at the valves in shift valve system 119 of FIG.IV, therein is a main pressure regulator valve 352, a 1-3 synchroselector valve 354, a 2-4 synchro selector valve 356, a reverse synchroselector valve 358, a double or piggyback trimmer valve 360 including a1-3 powershift clutch trimmer valve 362 and a 1st speed synchronizerclutch trimmer valve 364, a double trimmer valve 366 including a2-4-reverse powershift clutch trimmer valve 368 and a 2nd speedsynchronizer clutch trimmer valve 370, 3rd and 4th speed synchronizerclutch trimmer valves 372 and 374, clutch selector valves 376 and 378,and a fourth gear signal valve 380.

Synchro selector valves 354, 356, and 358 port regulated pressure totheir associated synchro actuators in response to the absence orpresence of hydraulic pressure in lines 264, 292, and 304 from hydrauliclogic 118. Powershift clutch trimmers 362 and 368 in double trimmervalves 360 and 366 control the on coming rate of friction clutches 48and 82 by controlling the rate of pressure rise of the hydraulicpressure actuating the friction clutches. Synchronizer clutch trimmervalves 364, 370, 372, and 374 control the rate of pressure rise insynchro actuators 61 and 97. Selector valves 376 and 378 port pressureto and from their associated powershift friction clutches to actuate andrelease the clutches in response to the presence and absence of pressurein lines 248 and 250 from hydraulic logic 118. Fourth gear signal valve380 effects a lowering of the regulated pressure from regulator valve352 when the transmission is to be shifted into the fourth speed ratio.

Main Pressure Regulator Valve 352

Valve 352, which is shown enlarged in FIG. IV-A, includes a stepped bore382 having bore portions 382a-382e of successively increasing diameter,annular ports 352a-352f, a stepped spool 384 having lands 384a-384f,springs 386 and 388 biasing the spool upward, an open centered member390 secured in the bore by a snap ring to provide a reaction surface forthe springs and a vent for the space containing the springs, a spacertube 392 supported by member 390 and operative to limit downwardmovement of the spool, and a plug 394 secured in the bore by a snap ringfor sealing the top of bore portion 382a and limiting upward movement ofthe spool. A drilled passage 384g in spool 384 communicates the spacebetween lands 384b and 384c with the space between the top of spool 384and plug 394. Lands 384a-384c are equal diameter and lands 384d-384f areof successively increasing diameter. Land 384c includes axiallyextending notches 384i to ensure at least a restricted flow of oil fromport 352b to port 352c when spool 384 is in the full upward position, asshown. Port 352a communicates via a line 396 with an unshown sump. Port352b communicates via a line 398 with pressurized oil from pump 34. Port352b also directly communicates via a main pressure line 400 and severalsame numbered branch lines with annular ports 354a and 354e of selector354, with annular ports 356a and 356e of selector 356, with an annularport 358c of selector 358, with an annular port 376a of selector 376,and with an annular port 378a of selector 378. Port 352c communicatesvia a line 402 with torque converter 22 in a conventional manner. Port352d communicates via a line 404 with port 314b of actuator 61, with anannular port 354b of selector 354, and with an annular port 372a oftrimmer 372. Port 352e communicates via a line 406 with a nonannularport 380c of valve 380. And port 352f communicates via a line 408 withport 340a of actuator 116 and with annular port 358b of selector 358.

The force of springs 386 and 388 and the counter force of hydraulicpressure acting on the top of spool 384 varies the amount of oilcommunication from port 352b to port 352a to regulate the hydraulic oilpressure in main pressure line 400 at a first desired amount, forexample 340.0 psi (23.0 kg/cm². The first main line pressure is reducedto lower levels when valves 354, 380, and 358 communicate hydraulicpressure to ports 352d, 352e, and 352f via lines 404, 406, and 408,respectively. Pressure at these ports acts on the spool shouldersdefined by the difference in diameter of lands 384c-384f and applies adownward force on the spool to increase communication between ports 352aand 352b, thereby dumping a greater volume of oil flow to sump line 396to decrease the pressure in main line 400.

1-3 Synchro Selector Valve 354

Valve 354, which is shown enlarged in FIG. VI-B, includes a bore 410having a relatively long bore portion 410a and a bore portion 410b ofslightly greater diameter threaded at its lower end, annular ports354a-354e, a spool 412 having lands 412a-412c, a spring 414 biasing thespool downward and reacting against a retainer pin 416 which limitsupward movement of the spool, and an adapter 418 threaded into thethreads of bore portion 410b until the top end 418a of the adaptersealing abuts the shoulder defined by the difference in diameter of boreportions 410a and 410b. The axial center of adapter 418 receives line304 from logic system 118 for directing pressurized oil via arestriction 418b to and from the space between adapter end 418a and thebottom end of the spool. Adapter end 418a also limits downward movementof the spool by spring 414. As previously mentioned, ports 354a and 354ecommunicate directly with main pressure line 400; port 354b communicatesdirectly with port 314b of actuator 61, with port 372a of trimmer 372,and with port 352d of regulator 352, respectively. Port 354ccommunicates with an exhaust 420. And port 354d communicates via a line422 with a port 364a of trimmer 364 and with a port 314a of actuator 61.

In the absence of pressurized oil to the bottom of spool 412 via line304 from logic 118, spring 414 maintains the spool in the downwardposition, as shown in FIG. IV. Hence, land 412a blocks port 354a; thespace between lands 412a and 412b communicates port 354b with exhaust420 via port 354c, thereby communicating port 314b of actuator 61 andports 372a and 352d of valves 372 and 352 to exhaust 420 via line 404;and the space between lands 412b and 412c communicates port 354d withports 354e, thereby communicating oil from main pressure line 400 vialine 422 with port 314a of actuator 61 and with port 364a of trimmervalve 364. Trimmer valve 364 dumps decreasing amounts of oil from line422 to an exhaust 424 for controlling the rate of pressure rise at port314a of synchro actuator 61 in a manner to be described thereinafter.

The presence of pressurized oil to the bottom of spool 412 via line 304shifts or shuttles the spool upward until the top of the spool contactspin 416, as shown in FIG. IV-B. With the spool in the up position thespace between lands 412a and 412b communicates port 354a with port 354b,thereby communicating oil from main pressure line 400 via line 404 withport 352d of regulator 352 to reduce main line pressure in a mannerpreviously described, with port 314b of synchro actuator 61, and withport 372a of trimmer valve 372. Trimmer valve 372, which is functionallysimilar to trimmer 364, dumps decreasing amounts of oil from line 404 toan exhaust 426 for controlling the rate of pressure rise at port 314b ofsynchro actuator 61. Also, in the up position of spool 412, land 412cblocks main line pressure at port 354e and the space between lands 412band 412c communicates port 354d with port 354c, thereby communicatingport 364a of trimmer 364 and port 314a of synchro actuator 61 to exhaust420.

2-4 Synchro Selector Valve 356

Valve 356 is identical in construction to valve 354. Hence, it shouldsuffice to merely describe oil communications provided by the downwardand upward positions of a spool 428 and lands 428a-428c defined therebyin cooperation with ports 356a-356e from top to bottom of valve 356. Inthe downward position of spool 428 (as shown, due to the absence ofpressurized oil in line 292 from logic 118) land 428a blocks port 356a;the space between lands 428a and 428b communicates port 356b with port356c and an exhaust 430, thereby communicating a port 380a of fourthspeed signal valve 380, port 326c of actuator 97, and a port 374a oftrimmer 374 with exhaust 430 via a line 432; and the space between lands428b and 428c communicates port 356d with port 356e, therebycommunicating oil from main pressure line 400 via a line 434 with a port370a of trimmer 370 and with port 326b of actuator 97. Trimmer valve370, which is functionally similar to trimmers 364 and 372, dumpsdecreasing amounts of oil from line 434 to an exhaust 435 forcontrolling the rate of pressure rise at port 326b of synchro actuator97 in a manner to be described hereinafter.

The presence of pressurized oil in line 292 shifts spool 428 upward suchthat the space between lands 428a and 428b communicates port 356a withport 356b, thereby communicating oil from main pressure line 400 vialine 432 with ports 380a, 374a, and 326c. Trimmer valve 374, which isfunctionally similar to trimmers 364, 372, and 370 dumps decreasingamounts of oil from line 432 to an exhaust 436 for controlling the rateof pressure rise at port 326c of synchro actuator 97 in a manner to bedescribed hereinafter.

Reverse Synchro Selector Valve 358

Valve 358 is also identical in construction to valves 354 and 356.Hence, as with the discussion of valve 356, it should suffice to merelydescribe oil communications provided by the downward and upwardpositions of a spool 438 and lands 438a-438c defined thereby incooperation with ports 358a-358e from top to bottom of valve 358. In thedownward position of spool 438 (as shown, due to an absence ofpressurized oil in line 264 from logic 118) land 438a blocks port 358awhich communicates with an exhaust 440; the space between lands 438a and438b communicates port 358b with port 358c, thereby communicating oilfrom main pressure line 400 via line 408 with port 340a of actuator 116and with port 352f of regulator 352; and the space between lands 438band 438c communicates port 358d with port 358e which is connected to anexhaust 442, thereby communicating exhaust 442 with port 380e of valve380, with port 340b of actuator 116, and with port 326a of actuator 97via a line 444.

The presence of pressurized oil in line 264 shifts spool 438 upward suchthat the space between lands 438a and 438b communicate port 358a withport 358b, thereby communicating ports 352f and 340a with exhaust 440via line 408; the space between lands 438b and 438c communicates port358c with port 358d, thereby communicating oil from main pressure line400 with ports 380e, 340b and 326a via line 444; and land 438c blocksport 358e.

Selector Valve 376

Valve 376, which is shown enlarged in FIG. IV-C, includes a stepped bore446 having a relatively long bore portion 446a and a bore portion 446bof slightly greater diameter threaded at its upper end, annular ports376a-376c, a spool 448 having lands 448a and 448b, a spring 450 biasingthe spool upward and reacting against a retainer pin 452 which limitsdownward movement of the spool, and an adapter 454 threaded into boreportion 446b until the bottom end 454a of the adapter sealing abuts theshoulder defined by the difference in diameter of bore portions 446a and446b. The axial center of adapter 454 receives line 248 from logicsystem 118 for directing pressurized oil via a restriction 454b to andfrom the space between adapter end 454a and the top of the spool.Adapter end 454a also limits upward movement of the spool by spring 450.Land 448a is provided with an annular groove 448c and one or more axialnotches or restrictions 448d for connecting the space between lands 448aand 448b to port 376c when the spool is in the upward position. When thespool is fully down, as shown in FIG. IV-C, the portion of land 448aabove groove 448c blocks port 376c. Port 376c communicates with anexhaust 456. Port 376b communicates via line 69 with friction clutch 48in FIG. I and with an annular port 362a of trimmer 362. And port 376acommunicates directly with main pressure line 400. Trimmer valve 362,which is functionally similar to the previously mentioned trimmervalves, dumps decreasing amounts of oil from line 69 to an exhaust 458for controlling the rate of pressure rise in clutch 48.

In the absence of pressurized oil to the top of spool 448 via line 248from logic system 118, spring 450 maintains the spool in the upwardposition, as shown in FIG. IV. Hence, land 448b blocks main linepressure at port 376a and line 69 communicates with exhaust 456 via thespace between lands 448a and 448b, restrictions 448d, groove 448c, andport 376c, whereby clutch 48 is released or unapplied.

The presence of pressurized oil to the top of spool 448 via line 248,shifts or shuttles the spool downward against pin 452, as shown in FIG.IV-C. With the spool in the downward position land 448a blocks port 376cand the space between lands 448a and 448b communicates port 376a withport 376b, thereby communicating oil from main pressure line 400 vialine 69 with port 362a of trimmer 362 and with clutch 48 to engage theclutch and effect completion of a shift into either the first or thirdspeed ratios.

Selector Valve 378

Valve 378 is identical in construction to valve 376. Hence, it shouldsuffice to merely describe oil communication provided by the upward anddownward positions of a spool 460 and its lands 460a and 460b incooperation with ports 378a-378c from bottom to top of valve 378. Port378a communicates directly with main pressure line 400. Port 378bcommunicates via the line 103 with a nonannular port 380d of signalvalve 380, with an annular port 368a of trimmer 368, and with frictionclutch 82 in FIG. I. Port 378c communicates with an exhaust 462. Trimmervalve 368, which is functionally similar to the previously mentionedtrimmer valves, dumps decreasing amounts of oil from line 103 to anexhaust 464 for controlling the rate of pressure rise in clutch 82.

In the upward position of spool 460 (as shown in FIG. IV, due to theabsence of pressurized oil in line 250 from logic system 118) land 460bblocks oil from main pressure line 400 at port 378a, and line 103communicates with exhaust 462 via the space between lands 460a, and 460band a groove and restrictions in land 460a as in valve 376, wherebyclutch 82 is disengaged. In the downward position of spool 460 port 378cis blocked by land 460a and the space between lands 460a and 460bcommunicates port 378a with port 378b, thereby communicating oil frommain pressure line 400 via line 103 with port 380d of valve 380, withport 368a of trimmer 368 and, with clutch 82 to engage the clutch andeffect completion of shifts into either the reverse, second, or fourthspeed ratios.

Fourth Gear Signal Valve 380

Valve 380, which is shown enlarged in FIG. IV-D, communicates main linepressure to port 352e of regulator 352 to reduce main line pressure whenspool 460 of clutch selector valve 378 is shifted downward to applyclutch 82 for a fourth speed ratio upshift. Valve 380 includes a steppedbore 466 having bore portions 466a and 466b, ports 380a-380e, a spool468 having lands 468a and 468b, and a spring 470 biasing the spoolupward against a shoulder formed by the difference in diameter of boreportions 466a and 466b. Spring 470 reacts against a plug 472 sealing thelower end of bore portion 466b. The top of bore portion 466a is blind.As previously mentioned, port 380a communicates via line 432 with port356b of 2-4 synchro selector 356, port 380c communicates via line 406with port 352e of regulator 352, port 380d communicates via line 103with port 378b of selector valve 378, and port 380e communicates vialine 444 with port 358d of reverse selector valve 358. Port 380bcommunicates with an exhaust 474.

When spool 468 is in the upward position, as shown in FIG. IV, the spacebetween lands 468a and 468b communicates line 406 with exhaust 474 andland 468b blocks port 380d. Spool 468 is shifted downward by thepresence of pressurized oil at port 380a from 2-4 synchro selector valve356 in response to an upward shift of spool 428 therein. Spool 428 ofvalve 356 is shifted up to initiate shifts into both the fourth andreverse speed ratios. With spool 468 in the downward position as shownin FIG. IV-D, the space between lands 468a and 468b communicates line103 with line 406 via ports 380c and 380d and land 468a blocks port380b. Hence, when spool 460 of selector valve 378 is shifted downward tocomplete a fourth speed ratio shift, pressurized oil from line 103 flowsto port 352e to reduce main line pressure in response to the oilpressure acting downward on the shoulder defined by the difference indiameter of lands 384d and 384e of spool 384.

During a reverse speed ratio shift, when logic system 118 applies oilpressure to line 264 to move the spool of reverse selector valve 358upward to initiate engagement of reverse synchronizer-jaw clutch 84, thelogic also applies oil pressure to line 292 to move the spool in 2-4synchro selector 356 upward, thereby communicating main line pressure toline 432 to ensure neutral positioning of piston 332 in 2-4 synchroactuator 97, as previously explained. The pressure in line 432, whichwould normally move the spool in valve 380 down, is countered by mainline pressure applied to port 380e via line 444 from reverse selectorvalve 358, this pressure in combination with the force of spring 470maintains spool 468 in the up position.

Third Speed Synchro Trimmer Valve 372

Valve 372, as previously mentioned, controls the rate of pressure risein line 404 connecting 1-3 synchro selector 354 with port 314b of 1-3synchro actuator 61, thereby controlling the rate of pressure riseacting on the left side of piston 320 and the engaging force of thesynchronizing friction clutch portion of 1-3 synchronizer-jaw clutch 42while third speed ratio gear 46 is being synchronized with countershaft40. Hence, when the friction clutch portion is first engaged and thespeed difference between the gear and countershaft is the greatest, theengaging force of the synchronizing friction clutch portion isrelatively low. The pressure and engaging force then rises over apredetermined time period while the speed difference decreases to zeroor synchronism. By controlling or increasing the engaging force of thesynchronizer clutch as the speed difference thereacross diminishes theinstantaneous horsepower absorbed by the synchronizer clutch ismaintained relatively constant during the synchronizing period.

Valve 372, which is shown enlarged in FIG. IV-E, includes a stepped bore476 having a relatively long bore portion 476a and a relatively shortbore portion 476b of smaller diameter; annular ports 372a and 372b; astepped spool 478 having lands 478a and 478b, an extension 478c, and arestricted passage 478d; and a piston 480 biased against extension 478cby a spring 482 reacting against a plug 484 secured in bore portion476a. Plug 484 includes an open centered extension which limits downwardtravel of piston 480 and vents the space containing spring 482 toexhaust. As previously mentioned, port 372a communicates with line 404.Port 372b communicates with the exhaust 426.

When spool 478 is in the full upward position, as shown in FIG. IV, land478b blocks communication between ports 372a and 372b. As spool 478moves downward, land 478b moves out of sealing contact with bore portion476b, thereby allowing oil communication from port 372a to exhaust 426via port 372b to regulate the pressure rise of oil in line 404 andaccordingly the force acting on piston 320 of actuator 61. When spool412 in 1-3 synchro selector valve 354 is shifted upward, oil from mainpressure line 400 flows via line 404 to the left side of piston 320 andto port 372a. The oil pressure on the left side of piston 320 and atport 372a simultaneously and quickly builds up to a first predeterminedlevel sufficient for the oil pressure acting on the smaller diameter ofthe spool to counter the upward force of spring 482 and move the spooldownward enough to effect oil flow from port 372a to exhaust 426. At thesame time the pressurized oil flows through restricted passage 478d ofspool 478 into the space between the spool and piston 480. As seen inFIG. IV-E, the oil gradually separates the spool and piston as itsvolume increases, thereby increasing the upward force acting on thespool as the spring 482 compresses. The spool moves upward in responseto the increasing upward force and gradually reduces the amount of oilflow to exhaust 426, thereby increasing the pressure in line 404 andaccordingly the force acting on piston 320 at a rate determined by thesize of restriction 478d and the spring rate of spring 482.

A graph in FIG. V illustrates the pressure rise in line 404 with respectto time. The pressure rises rather quickly to a first predeterminedlevel A; the pressure then rises along a path to a level B at ratecontrolled by the size of restriction 478d and the spring rate of spring482. At level B oil flow to exhaust 426 is completely blocked by land478b; hence, the oil pressure then rises abruptly to main line pressureat a level C. The path between levels A and B, shown as linear forsimplicity in FIG. V, may be curved.

As previously mentioned, transmission 10 is a preselection transmissionwherein the synchronizer-jaw clutch for the next upshift or downshift ismoved from one ratio engaging position to another while its respectivepower shift friction clutch 48 or 82 is disengaged and drive is throughanother synchronizer-jaw clutch on the other countershaft. That is, whenthe synchronizer-jaw clutches are shifted between ratio positions theengaged jaw clutch portion therein is not transmitting torque and istherefore moved out of engagement by its respective actuator in responseto relatively low oil pressures equal to or slightly below pressurelevel A in FIG. V. More specifically, when pressurized oil iscommunicated to the left side of piston 320, pressure levels below levelA move the piston rightward to disengage the jaw clutch portion ofclutch 42 coupling first speed ratio gear 44 to countershaft 40; thepiston continues to move rightward engaging the synchronizer and blockerportions of clutch 42; the synchronizer portion frictionally couplesthird speed ratio gear 46 to countershaft 40 at or about pressure levelA and the blocker portion prevents engagement of the jaw clutch portion;thereafter, the pressure rises along the curve from level A to level B.By the time the pressure reaches level B synchronism is reached, wherebythe blocker portion of clutch 42 unblocks and allows engagement of thejaw clutch portion of clutch 42 to effect a positive coupling betweenthird speed ratio gear 46 and countershaft 40.

Prior art trimmer valves, similar to valve 372, have been used tocontrol the rate of pressure rise in powershift clutches such asclutches 48 and 82. Therein, the purpose of the trimmer was to controlshift smoothness when shifting between ratios. Herein, the trimmercontrols the instantaneous amount of horsepower absorbed by thesynchronizer portion of clutch 42 at or near an amount which willminimize wear of the friction surfaces of the synchronizer portion whileat the same time maintaining a relatively short synchronizing period.For example, friction materials such as bronze against steel have beenfound to have a maximum wear lift when the instantaneous horsepowerabsorbed is less than 0.5 horsepower per square inch of frictionsurface.

Fourth Speed Synchro Trimmer Valve 374

Valve 374 is identical structurally and functionally to valve 372.Hence, it should suffice to say that valve 374 controls pressure rise inline 432 to maintain the horsepower absorbed by the synchronizer portionof clutch 74 at less than 0.5 horsepower per square inch of frictionsurface while fourth speed ratio gear 78 is being synchronized withcountershaft 72.

Combination Trimmer Valve 360

Valve 360, as previously mentioned, includes 1-3 powershift clutchtrimmer valve 362 and 1st speed synchronizer clutch trimmer valve 364for respectively controlling the rate of pressure rise in line 69 toclutch 48 and the rate of pressure rise in line 422 to synchro actuator61. The purpose of valve 364 is the same as valves 372 and 374. Thepurpose of valve 362 is the same as other prior art trimmer valves, thatis, to control shift smoothness when shifting between ratios withpowershift friction clutches such as clutches 48 and 82. However, sincethe powershift friction clutches in transmission 10 each couple two ormore speed ratios, a single trimmer pressure rise or pressure schedulesuch as shown in FIG. V provides less than desired results. As may beseen in FIG. VI, valve 362 is constructed in combination with valve 364such that the rate of pressure rise in line 69 follows a curve or pathD, E, F when clutch 48 is being engaged to complete a first speed ratioshift and follows a curve or path G, H, F' when clutch 48 is beingengaged to complete a third speed ratio shift. Pressure paths D, E, Fand G, H, F' correspond to force paths for controlling the oncomingengagement rate of powershift clutch 48.

Valve 360 is shown enlarged in FIG. IV-F. Valves 362 and 364 arecontained in a common stepped bore 486 having a short bore portion 486aand a relatively long bore portion 486b of greater diameter. Valve 362includes annular ports 362a and 362b; the exhaust 458 connected to port362b; a stepped spool 488 having lands 488a and 488b, a short extension488c, and a restricted passage 488d; and a piston 490 biased upward by apreloaded spring 492 which also biases a piston 494 of valve 364downward. The space between pistons 490 and 494 is vented to an exhaust496 and also contains a free length spring 498 and a stop or spacersleeve 500. Valve 364, which is disposed in bore 486 in mirror imagefashion with respect to valve 362, includes an end cap 502, a steppedspool 504, the piston 494, ports 364a and 364b, the exhaust 424connected to port 364b, and the springs 492 and 498 shared with valve362. End cap 502, which is secured in the bottom of bore portion 486b bya snap ring, includes a bore portion 502a analogous to bore portion486a, a plurality of passages 502b connected with an annular groove 502cfor communicating bore portion 502a with port 364a, and an extensionportion 502d having a stop nut 506 at its upper end. Stepped spool 504includes lands 504a and 504b, a central opening 504c slidably andsealingly receiving extension 502d, a raised ring portion 504d analogousto extension 488c and a restricted passage 504e. Piston 494 includes acentral opening 494a slidably and sealingly receiving extension 502d.

Trimmer valve 364 is functionally substantially the same as trimmervalve 372. When 1-3 synchro selector 354 communicates main pressure line400 with line 422, spool 504 moves upward and land 504a moves out ofsealing contact with bore portion 502a, thereby allowing oilcommunication from port 364a to exhaust 424 to regulate the pressurerise of oil in line 422 and accordingly the force acting on piston 320of synchro actuator 61. At the same time, the pressurized oil acting onspool 504 flows through restricted passage 504e into the space betweenspool 504 and piston 494. The oil gradually separates the spool andpiston as its volume increases, thereby increasing the downward forceacting on the spool as piston 494 moves upward toward stop nut 506.Upward movement of piston 494 first compresses spring 492 and thenspring 498 just before the stop nut arrests further upward movement ofthe piston. The pressure rise in line 422 is substantially as shown inFIG. V. When piston 494 contacts the stop nut, the oil pressure betweenthe spool and piston quickly rises to the oil pressure level on thelower side of the spool. Since the upper surface area of the spool isgreater than the lower surface area, the spool moves downward and land504a moves into sealing contact with bore portion 502a.

Looking now at valve 362, when clutch selector valve 376 communicatesmain pressure line 400 with line 69, spool 488 moves downward and land488a moves out of sealing contact with bore portion 486a, therebyallowing oil communication from port 362a to exhaust 458 to regulate theoil pressure in line 69 at a first or second initial level determined bythe smaller diameter area of spool 488 and the initial or preload forceof the spring(s) acting on piston 490. When piston 494 of valve 364 isin the downward position shown in FIG. IV, the first initial levelcoincides with point G in FIG. VI. When spool 494 is in the up positionagainst stop nut 506, as shown in FIG. IV-F, the second initial levelcoincides with point D in FIG. VI. The pressurized oil acting on thesmaller diameter area of spool 488 also flows through restricted passage488d into the space between the spool and piston 490. The oil graduallyseparates the spool and piston as its volume increases, therebyincreasing the upward force acting on the spool as piston 490 movesdownward toward stop sleeve 500. When piston 494 is in the downposition, downward movement of piston 490 first compresses spring 492and then spring 498. When piston 494 is in the up position, both springsare compressed during full downward travel of piston 490. When piston490 contacts the stop sleeve, the oil pressure between the spool andpiston quickly rises to the oil pressure level acting on the top orsmaller diameter surface area of spool 488. Since the lower surface areaof the spool is greater than the upper surface area, the spool movesupward and land 488a moves into sealing contact with bore portion 486a.From the foregoing it should be clear that piston 494 functions as apressure control means for valve 362. When piston 494 is down theextension of springs 492, 498 are a maximum and the fluid pressure atport 462a rises along path G, H, F'. When the piston is up, theextension of spring 492, 498 are a minimum and the pressure at port 462arises along path D, E, F.

Looking now at a transmission shift in to the first speed ratio, e.g., adownshift into the first speed ratio, logic system 118 anticipates thedownshift and sends a first speed signal to 1-3 synchro selector valve354 in the form of an absence of pressure in line 304, whereby the spoolin valve 354 moves downward and communicates main pressure line 400 withtrimmer valve 364 and synchro actuator 61 via line 422. Trimmer valve364 regulates the pressure rise in line 422 in accordance with curve A,B, C in FIG. V while piston 320 moves synchronizer-jaw clutch 42leftward to synchronize and jaw clutch first speed ratio gear 44 withcountershaft 40 over a predetermined time period. Following this periodand while piston 494 is in the up position against stop nut 506, thelogic system sends another first speed shift signal to clutch selectorvalve 376 in the form of an absence of pressure in line 248, whereby thespool in valve 376 moves upward and communicates main pressure line 400with trimmer valve 362 and power shift clutch 48 via line 69. Sincesprings 492 and 498 are partially compressed, the pressure in line 69rises in accordance with curve D, E, F in FIG. VI, thereby providing asmooth and controlled rate of engagement of clutch 48 for a first speedratio shift.

When the transmission is shifted into the third speed ratio, the spoolin 1-3 selector valve is up and trimmer valve line 422 is communicatedwith exhaust 420. Hence, piston 494 is down, whereby pressure in line 69rises in accordance with curve G, H, F' in FIG. VI.

Combination Trimmer Valve 366

Valve 366, as previously mentioned, includes 2-4 powershift clutchtrimmer valve 368 and 2nd speed synchronizer clutch trimmer valve 370which are identical in structure and function to valves 362 and 364 withthe exception of an additional annular port 370c. Port 370c communicatesthe space between the piston and spool of valve 370 with line 444 via acheck valve 508 which allows oil flow from line 444 into the spacebetween the piston and spool and prevents flow therefrom into line 444.Hence, the springs biasing the piston of valve 368 are partiallycompressed when a shift into second and reverse is made. Valve 370regulates the pressure rise in line 434 in accordance with curve A, B, Cin FIG. V. When power shift friction clutch 82 is being engaged tocomplete a shift into second or reverse, valve 368 regulates thepressure rise in line 103 to clutch 82 in accordance with curve D, E, Fin FIG. VI. When clutch 82 is being engaged to complete a shift intofourth, valve 368 regulates the pressure in accordance with curve G, H,F' in FIG. VI.

Alternative Embodiment

Components in the alternative embodiment FIG. VII which are the same ascomponents in previously discussed figures will be given the samereference numbers suffixed with a prime.

Looking at FIG. VII, therein is shown a trimmer valve 600 which may beused in lieu of combination trimmer valves 360 and 366 in shift valvesystem 119 of FIG. IV when the system is employed without synchronizerclutch trimmer valves 364, 370, 372, and 374 to control or maintain theinstantaneous horsepower into the synchronizer clutches relativelyconstant. When valve 600 is used, valves 372 and 374 are deleted andvalve 360 and 366 are each replaced by a valve 600. Valve 600 iscontained in a stepped bore 602 having bore portions 602a-602c ofsuccessively increasing diameter and annular ports 600a-600c; a steppedspool 604 having lands 604a and 604b, a short extension 604c, and arestricted passage 604d; a piston 606 biased upward by a preloadedspring 608 reacting at its lower end against a downwardly biased piston610 having a short extension 610a; and an end cap 612. The space betweenpistons 606 and 610 is vented to an exhaust 496' and also contains afree length spring 614. Piston 610 controls the maximum and minimumextension of springs 608 and 614. When valve 600 is used in lieu ofvalve 366, ports 600a and 600b are respectively connected to a line 103'and an exhaust 464', and port 600c is connected via a line 616 to anoutlet port 618a of a schematically illustrated shuttle valve 618. Theshuttle valve, which replaces check valve 508, includes inlet ports 618band 618c respectively connected to lines 434' and 444'. A shuttle ball620 is slidably disposed in a passage 618d connected at its ends toports 618b and 618c, and at its center to port 618a. The ball moves leftto block port 618c in response to oil pressure at port 618b and movesright to block port 618b in response to oil pressure at port 618c.

Valve 600 is functionally the same as valve 368 in valve 366 in that itprovides two different pressure rise schedules for oil pressure in line103'. When system 119 functions to engage powershift clutch 82 tocomplete a shift into second or reverse, the respective synchronizerengaging lines 434' or 444' are pressurized. Hence, shuttle valve 618directs pressurized oil to port 600c to move piston 610 up against theshoulder defined by the difference in diameter of bore portions 602b and602c, thereby further preloading spring 608 and also preloading spring614 with a resultant pressure rise schedule in line 103' along path D,E, F as shown in FIG. VI. When system 119 functions to engage powershiftclutch 82 to complete a shift to fourth, lines 434' and 444' are bothvented. Hence, piston 610 is in the down position with a resultantpressure rise schedule in line 103' along path G, H, F' as shown in FIG.VI.

When valve 600 is installed in lieu of valve 362 in valve 360, shuttlevalve 618 is dispensed with and lines 69 and 422 of system 119 arerespectively connected to ports 600a and 600c.

The control system embodiment and alternative valve embodiment thereforehave to be disclosed for illustrative purposes. Many variations of thedisclosed embodiments are believed to be within the spirit of theinventions therein. The following claims are intended to cover inventiveportions of the disclosed embodiments and modifications believed to bewithin the spirit of the inventions therein.

What is claimed is:
 1. In a powershift, preselect transmission of thetype including a plurality of multiple ratio gear power pathsalternately connectable between input and output shafts by firstengaging selected ones of clutch means associated with each gear andthen alternately engaging a powershift clutch associated with each pathand an improved control system comprising:a shift selector moveablebetween forward, neutral, and reverse positions; signal means providinga speed signal proportional to the output shaft speed; and reversesequence means shiftable between states respectively effectingengagement and disengagement of said one clutch means associated with areverse speed ratio gear of one of said paths and operative once shiftedinto said engagement state to continuously latch said one clutch meanstherein while said speed signal is below a predetermined magnitude andindependent of said shift selector position.
 2. In a powershift,preselect transmission of the type including a plurality of multipleratio gear power paths alternately connectable between input and outputshafts by first engaging selected ones of clutch means associated witheach gear and then alternately engaging a powershift clutch associatedwith each path and an improved control system comprising:a shiftselector moveable between forward, neutral, and reverse positions;signal means providing a speed signal proportional to the output shaftspeed; first means for selectively effecting engagement of the clutchmeans and alternately effecting engagement of the powershift clutches inresponse to the position of said shift selector; second means foreffecting engagement of the clutch means associated with a forward speedratio gear of one of said paths independent of said shift selectorposition; and reverse sequence means shiftable between statesrespectively effecting engagement and disengagement of said one clutchmeans associated with a reverse speed ratio gear of another of saidpaths and operative once shifted into said engagement state tocontinuously latch said one clutch means therein while said speed signalis below a predetermined magnitude and independent of said shiftselector position.
 3. The transmission of claim 2, said first and secondmeans are also responsive to changes in the magnitude of said speedsignal.
 4. The transmission of claim 1, 2, or 3, wherein said clutchmeans includes synchronizer clutches, said synchronizer and powershiftclutches are engaged by a regulated fluid pressure controlled by saidcontrol system, said signal means provides a proportional fluid pressuredefining said speed signal, and said reverse sequence means includes:areverse sequence valve having a valving member moveable between saidengagement and disengagement states for respectively allowing andblocking flow of the regulated pressure to effect said engagement anddisengagement of the synchronizer clutch associated with the reversegear, said valving member biased toward said disengagement state by saidproportional pressure and latched in said engagement state by saidregulated pressure once shifted into said engagement state so long assaid proportional pressure is below said predetermined magnitude.
 5. Ina transmission of the type including input and output shafts; aplurality of power paths disconnectable from both shafts; a plurality offorward speed ratio gears associated with one path and in constantdriving relation with one of the shafts; at least one forward and onereverse speed ratio gear associated with another path and in constantdriving relation with the one shaft; clutch means associated with eachgear and selectively engageable to connect one of the gears with theassociated path while the path is otherwise disconnected from theshafts; a powershift clutch associated with each path and alternatelyengageable to complete driving connections between the shafts via theselected one gears for up, down, and reverse shifting the transmission;an improved control system comprising:a shift selector means moveablebetween forward, neutral, and reverse positions; signal means providinga signal proportional to the output shaft speed; means operative toeffect the selective engagements of the clutch means and the alternateengagements of the powershift clutches in response to the position ofsaid selector means and changes in the magnitude of said speed signal;means operative to effect engagement of the clutch means associated withone forward speed ratio gear associated with the one path independent ofthe shift selector positions; and reverse sequence means shiftablebetween states respectively effecting engagement and disengagement ofthe clutch means associated with the reverse gear in the other path andoperative once shifted into said engagement state to provide a latchingsignal maintaining said state while said speed signal is below apredetermined magnitude and independent of changes in said shiftselector position, whereby the transmission may be powershifted betweenforward and reverse in response to movement of the selector mean betweensaid forward and reverse positions.
 6. The transmission of claim 5,wherein movement of the shift selector to said reverse position providesa reverse signal for shifting said reverse sequence means into saidengagement state.
 7. The transmission of claim 5, wherein movement ofthe shift selector to the reverse position provides a reverse signaloperative to shift said reverse sequence means into said engagementstate when the speed signal is below another predetermined magnitude. 8.The transmission of claim 6 or 7 further including:reverse timer meansenergized in response to initial shifting of said reverse sequence meansto said engagement state and operative when timed out to effectengagement of the powershift clutch associated with reverse gear powerpath.
 9. The transmission of claim 8, wherein timing out of said timermeans provides a second latching signal for latching of said reversesequence means in said engagement state when the speed signal is below athird predetermined level.
 10. The transmission of clutch 9, whereinsaid reverse signal and said latching signals additively cooperate tomaintain said engagement state.
 11. The transmission of claim 5, furtherincluding a regulated fluid pressure; wherein said signal means providesa proportional fluid pressure defining said speed signal; wherein saidselector means includes a valve connected to the regulated pressure andhaving a valving member moveable between said forward, neutral, andreverse positions and operative in said reverse position to direct theregulated pressure to a reverse signal line; and wherein said reversesequence means includes:a reverse sequence valve having a first portconnected to said regulated pressure, a second port connected to saidreverse signal line, a third port, and a valving member, said valvingmember biased by said proportional pressure toward a first positiondefining said disengagement state for blocking flow of the regulatedpressure to said third port and moveable to a second position definingsaid engagement state for allowing flow of said regulated pressure fromsaid first port to said third port in response to the presence ofregulated pressure in said reverse signal line and provided saidproportional pressure is below said predetermined amount.
 12. Thetransmission of claim 11, wherein said latching signal is defined bysaid regulated pressure at said third port.
 13. The transmission ofclaim 11 or 12, further including:a timer valve having a valving memberbiased toward a position blocking a port receiving regulated pressurefor effecting engagement of the powershift clutch associated with thereverse gear power path and moveable to an unblocking position over apredetermined time in response to regulated pressure at said third port.14. The transmission of claim 13, wherein the regulated pressureunblocked by said timer valve provides a second latching signal forlatching said valving member of said reverse sequence valve in saidsecond position when the proportional pressure is below a thirdpredetermined level.
 15. The transmission of claim 14, wherein theregulated pressure in said reverse signal line and said latching signalsadditively cooperate to maintain said valving member of said reversesequence valve in said second position.